1. Field of the Invention
The present invention relates to a solid state radiation detector having a charge storage section for storing an amount of electric charges as latent image charges that corresponds to the dose of radiation irradiated on the detector or the amount of light excited by the radiation and irradiated on the detector. The present invention is also directed to a method for testing such solid state radiation detector.
2. Description of the Related Art
Today, various types of radiation image recording/readout systems that use a solid state radiation detector (hereinafter also referred to as simply “detector”) are proposed in the field of radiation imaging for medical diagnosis and the like. The solid state radiation detector described above temporarily stores electric charges in the charge storage section as latent image charges obtained by detecting radiation, and outputs electrical signals representing the radiation image information by converting the latent image charges. Various types of detectors are proposed as the solid state radiation detector for use in such systems. From the aspect of charge reading out process in which charges stored in the detector are read out, some of the detectors are categorized into the optical readout type in which the charges are read out by irradiating readout light (readout electromagnetic wave) on the detector.
The inventor of the present invention has proposed a detector having a fast readout response along with an efficient signal charge readout capability as one of the optical readout type solid state radiation detector as described in U.S. Pat. Nos. 6,268,614, 6,770,901 and 6,518,575. The detector has a set of layers layered in the order of: a first conductive layer having transparency to recording radiation or light excited by the recording radiation (hereinafter referred to as “recording light”); a recording photoconductive layer that shows conductivity when exposed to the recording light; a charge transport layer that acts as substantially an insulator against charges having the same polarity as the charges charged on the first conductive layer and as substantially a conductor for the charges having the opposite polarity; a readout photoconductive layer that shows conductivity when exposed to readout light; a second conductive layer having transparency to the readout light. The layer composite has a charge storage section formed between the recording photoconductive layer and charge transport layer for storing latent image charges (electrostatic latent image) representing image information.
The solid state radiation detector proposed by the inventor of the present invention in U.S. Pat. Nos. 6,770,901 and 6,518,575, in particular, uses a stripe electrode constituted by multitudes of charge detecting linear electrodes having transparency to readout light as the electrode of the second conductive layer having transparency to readout light. In addition, the detector further includes multitudes of auxiliary electrodes for outputting electrical signals corresponding to the amount of latent image charges stored in the charge storage section. The auxiliary electrodes are opaque to readout light and provided in the second conductive layer such that they are arranged alternately and substantially in parallel with the charge detecting linear electrodes.
By providing the sub-stripe electrode constituted by the multitudes of auxiliary linear electrodes in the second conductive layer, a capacitor is newly formed between the charge storage section and sub-stripe electrode. This allows the transport charges having the opposite polarity to that of the latent image charges stored in the charge storage section by the recording light to be charged also on the sub-stripe electrode by the rearrangement of charges in the charge reading out process. This may reduce the amount of transport charges to be allocated to the capacitor formed between the stripe electrode and charge storage section with the readout photoconductive layer being sandwiched between them to relatively small compared with the case where no such sub-stripe electrode is provided. Consequently, the amount of signal charges which may be extracted from the detector to outside is increased and the readout efficiency is improved, resulting in a fast readout response with an efficient signal charge extraction capability.
In the mean time, when checking the stripe electrode (charge detecting linear electrodes) and sub-stripe electrode (auxiliary linear electrodes) for breakage, radiation imaging is performed first by irradiating radiation uniformly on the detector and then image signals are read out from the detector to see if there is any irregularity in the image signals in order to determine any breakage of the electrodes. This method requires a radiation exposure system for performing the test. Further, it requires a relatively long time since imaging and image signal reading out need to be performed for each solid state detector.
The present invention has been developed in view of the circumstances described above, and it is an object of the present invention to provide a solid state radiation detector having charge detecting linear electrodes and auxiliary linear electrodes in which checking of those electrodes for breakage may be performed easily.